Jesus identified Himself by saying literally "I am" (Gr. ego eimi). This is sometimes a way Jesus described Himself as God, as John recorded Jesus" words (e.g, John 8:24). However the clause does not always mean that since it is the normal way of identifying oneself (cf. John 9:9). In those instances the translation, "It is I," gives the intended meaning. Here Jesus was just identifying Himself to the disciples, though obviously someone who could walk on water was more than a mere man. [source][source][source]
Context Summary
John 6:15-21 - Jesus Brings Peace To Troubled Hearts
The most conclusive proof that our Lord was no weak fanatic or enthusiast is afforded by the calm temper which refused the eager impulse of the crowds to make Him king. Here the temptation of the wilderness was repeated; and only one who was filled with the unwavering determination to do God's will, could have refused this short cut to Messianic empire. Notice these withdrawals of our Lord to the calm of nature's stillness and the bosom of God. If he needed such spaces of undisturbed meditation and communion, surely we do.
He knew when he pressed the disciples into the boat, that the night would be full of storm, but He did not hesitate to expose them to its peril; he was conscious of His ability to turn that storm to the highest use by coming to their help. His advent is often delayed, but he always comes. Delays are not denials. He is as near in the storm as though already in the boat. The storm-waves are His pathway. Be not afraid! The people hurried across the Lake in the early morning, conveyed in the boats which had come to take them off; but as Jesus sorrowfully perceived, their object was to receive His gifts and not Himself. [source]
Chapter Summary: John 6
1Jesus feeds five thousand men with five loaves and two fishes 15Thereupon the people would have made him king; 16but withdrawing himself, he walks on the sea to his disciples; 26reproves the people flocking after him, and all the fleshly hearers of his word; 32declares himself to be the bread of life to believers 66Many disciples depart from him 68Peter confesses him 70Judas is a devil
Greek Commentary for John 6:20
Be not afraid [μη ποβειστε] Prohibition with μη mē and present middle imperative of ποβεομαι phobeomai So in Mark 6:50 (Matthew 14:27). John does not tell that the disciples thought Jesus was an apparition (Mark 6:49; Matthew 14:26), nor does he give the account of Peter walking on the water (Matthew 14:28-31). [source]
Reverse Greek Commentary Search for John 6:20
John 8:58Before Abraham was [πριν Αβρααμ γενεσται] Usual idiom with πριν prin in positive sentence with infinitive (second aorist middle of γινομαι ginomai) and the accusative of general reference, “before coming as to Abraham,” “before Abraham came into existence or was born.” I am Undoubtedly here Jesus claims eternal existence with the absolute phrase used of God. The contrast between γενεσται genesthai (entrance into existence of Abraham) and ειμι eimi (timeless being) is complete. See the same contrast between εν en in John 1:1 and εγενετο egeneto in John 1:14. See the contrast also in Psalm 90:2 between God See the same use of ειμι eimi in John 6:20; John 9:9; John 8:24,John 8:28; John 18:6. [source]
Greek Commentary for John 6:20
Prohibition with μη mē and present middle imperative of ποβεομαι phobeomai So in Mark 6:50 (Matthew 14:27). John does not tell that the disciples thought Jesus was an apparition (Mark 6:49; Matthew 14:26), nor does he give the account of Peter walking on the water (Matthew 14:28-31). [source]
Reverse Greek Commentary Search for John 6:20
Usual idiom with πριν prin in positive sentence with infinitive (second aorist middle of γινομαι ginomai) and the accusative of general reference, “before coming as to Abraham,” “before Abraham came into existence or was born.” I am Undoubtedly here Jesus claims eternal existence with the absolute phrase used of God. The contrast between γενεσται genesthai (entrance into existence of Abraham) and ειμι eimi (timeless being) is complete. See the same contrast between εν en in John 1:1 and εγενετο egeneto in John 1:14. See the contrast also in Psalm 90:2 between God See the same use of ειμι eimi in John 6:20; John 9:9; John 8:24, John 8:28; John 18:6. [source]